The invention concerns a proportional pressure control valve possessing a pressure reduction means and performs a pressure maintaining function. The valve is mainly comprised of a valve housing with inlet and outlet ports, a control element for the opening and closing of the valve seat or throttling orifice, an armature rod with an armature axis for connecting the control element with a proportional magnet, which latter is an assembly of a magnet core, a magnet armature and a magnet coil. The magnet armature is movable forward and back between two end positions, whereby the first position represents the hold position of the magnet armature, which means, that the magnet armature, by means of the control element is holding shut at least one valve seat.
A multiplicity of valves, of the above known mode of construction are known in the state of the technology. Such conventional valves are employed, for instance, as servo valves for the control of clutches in automatic transmissions of motor vehicles. In such transmissions, the principal hydraulic pressure, for example in the case of passenger car transmissions, runs about 10 bar or more. This principal pressure is normally reduced to a operating pressure of about 5 bar by a pressure reducing valve, to which the proportional pressure regulating valve is subjected. In order, for example, after the engagement of a clutch, to hold said clutch engaged, normally a safety over-pressure, which, more or less, represents the system pressure, is applied on the clutch cylinder and by means of additional holding valves, the necessary pressure is maintained. Following this arrangement, three valves, namely a proportional pressure regulator valve, a pressure reducing valve, and a pressure maintaining valve are necessary for operation, particularly in a clutch in an automatic transmission.
Thus it is the purpose of the invention, to make available a valve, which fulfills the above named functions, but in doing so, possesses a simpler design, for instance by having lesser components, and on this account is more economical to manufacture.
In accordance with the invention, the purpose will be achieved, in that, in the case of a proportional pressure control valve of the above type of construction, the smallest axial distance between the end surfaces of the magnet armature and the core of the magnet, is so dimensioned, that the magnetic force between the magnet armature and the magnet core, in this holding position, is greater than the magnetic force in the operating range of the proportional magnet. Further, the magnet armature, because of the excessive magnetic force in this holding position, can be sustained in its position. Advantageously, the invention makes use of the facts that a proportional magnet in its operating range exhibits a nearly horizontal force-thrust-line, and the magnetic force at a distance less than a certain thrust displacement, that is, a small distance between magnet armature and magnet core abruptly increases in comparison to the magnetic force in the operational range. In regard to the state of the technology, refer to Mannesmann-Rex-Roth: xe2x80x9cFluid Technik von A bis Zxe2x80x9d, xe2x80x9cDer Hydraulik Trainerxe2x80x9d, Vol. 5, 04.95, page 266. Employing this magnetic characteristic with great magnetic forces at very small air gaps, by means of appropriate magnet dispositions, a coil current, that is a xe2x80x9csnap-currentxe2x80x9d can be evoked, at which the operational range of the magnet is overstepped and the magnet armature is held within the field of the high magnetic force. By the connection of the magnet armature to the control element through the armature rod, the retaining force on the respectively closed valve seat of the control element is increased, so that this valve seat, even at an existing system pressure greater than 10 bar stays reliably closed. On this account, the achievement can be attained, that with the invented proportional pressure control valve, both a pressure reducing valve as well as a pressure retaining valve advantageously can be dispensed with, since their functions are collectively fulfilled by the invented valve. Further, a controller of this kind possesses, advantageously, a high pressure/current (p/l) ratio in its range of fine regulation between 0 and about 5 bar. Further, the holding function in accord with the invention, advantageously makes possible the blocking of masses inclined toward vibration in the pressure controller. Thus, stability as to oscillation is assured and the equipment is subject to mechanical wear only in a small degree.
In a preferred development of the invention, the control element possesses two control edges, which are designed as a flat seat and a slide edge. With such an arrangement, there is provided in a simple manner a cost effective design, especially of a 3/2-way pressure regulator with magnetic holding function of the magnet armature. In this design, the flat seat carries out the fulfillment of the pressure holding function and the pressure controller advantageously can be installed as a servo control element.
In a further development of the invention, the proposal is made, that between the magnet armature and the armature rod, a spring element be placed. For example this could be a screw spiral shaped compression spring. The achievement thereby gained is, that the armature rod does not directly contact the magnet armature, and further, a static redundancy between the flat seat of the control element and the end detent of the armature rod on the armature is compensated for.
Advantageously, the compression spring, which is placed between the armature rod and the magnet armature, exhibits a xe2x80x9chardxe2x80x9d spring characteristic curve, wherein an overrun of the proportional range of the magnet is reached, as well as a quick switch of the magnet armature out of the operational range into the holding position takes place and a reinforcement of the snap effect is realized. The spring force of the compression spring is, in this matter, chosen in such a manner, that it is greater or equal to the maximum hydraulic controlling force on the flat seat. This maximum, hydraulic control force corresponds to the product of the maximal, hydraulic control pressure multiplied by the nominal area of the flat seat.
Advantageously, as a result of this situation, the spring brings about a xe2x80x9csnap closure protectionxe2x80x9d in the hydraulic system. The Spring Rate of the compression spring is advantageously made as small as possible, so that even by a small coil current the magnet armature can be brought into the area of higher magnetic forces and thereby the holding function of the magnet armature is realizable. The magnet armature in this position is xe2x80x9csnapped toxe2x80x9d.
The compression spring is further so designed in regard to its spring characteristic line, as well as its spring geometry, including, for instance, the length of the spring, the diameter of the spring wire, etc., and the fastening of the spring between the armature and the armature rod is so chosen, that in the holding position of the magnet armature the smallest possible axial distance between the magnet core and the magnet armature can be made to lie in the range of 0 to 0.3 mm, preferably xe2x89xa60.1 mm. In the case of this distance, the magnetic force is sufficiently great as compared to the magnetic force in the operational range, so that the magnet armature, even during applied hydraulic principal pressure, advantageously remains in its end position.
Alternative to the above described realization of the least possible distance between the magnet core and the magnet armature, a spacer disk, made of a non-magnetic substance, can be inserted between the magnet core and the magnet armature. Such a spacer disk prevents a magnetic xe2x80x9cadhesionxe2x80x9d of the magnet armature on the magnet core. Also, by means of different construction of the thickness of said disk, advantageously a simple adjustment of the magnetic force becomes possible. Instead of a space disk, a non-magnetic coating can be provided on the magnet core and/or on the magnet armature, which assures a reliable holding of the axial distance between the magnet core and the armature.
In a particularly advantageous design, the distance between the end wall surface of the magnet core and that of the magnet armature, runs some 0.01 to 0.3 mm, preferentially, however, 0.10 mm. At this distance, already a sufficient magnetic holding force has been attained.
This maximum magnetic holding force, over the entire operational area of the pressure control valve, must be greater than that of the hydraulic force resulting from the maximum, hydraulic operational pressure. In yet another embodiment of the invention, the proposal is that the magnet coil be connected with an electrical control apparatus, which, in a predetermined, timely period, emits a current impulse to the magnet spool for the maintenance of the holding position of the magnet armature. In this way, assurance is given, that the magnet armature retains its holding position relative to the magnetic core and does not, without notice, xe2x80x9cfall outxe2x80x9d. And so, advantageously, the tight seat of the control element remains reliably closed.
It has proven itself to be of advantage, that the electrical current impulse generates a current strength, which is greater than the holding current of the magnet coil and for instance, amounts to about 950 mA. Further the said current impulse appears in time related intervening distances of, for example, 20 ms, since this duration has been determined to be the time period in which the magnet armature can drop out of its hold position.
For a considered release of the magnet armature from its holding position, the magnet coil is subjected to an electrical control signal, which is done, for instance, by a reduction and subsequent increase of the control current, (loop control) in said magnet coil. In this way, in a simple manner, a release of the armature can be accomplished in an elegant way.
Alternatively, an intended release of the magnet armature from its holding position can be carried out by a pressure signal, which, for example, is done by an increase of the hydraulic principal pressure above the holding pressure. This pressure increase, for instance, acts upon the flat seat of the control element. Thereby, in an advantageous manner, a release of the magnet armature from the magnet core is effected by means of a movement of the armature rod
Advantageously, the invented proportional pressure control valve can be used as a servo or relay valve. In this service the valve is preferentially designed as a 3/2-way proportional pressure control valve with a magnetic holding function of the magnet armature. This allows that, upon the use of the invented valve, both a pressure reducing valve, and a pressure sustaining valve can be dispensed with.
Alternatively, the invented proportional pressure controlling valve, can also be employed as a direct control valve, whereby the hydraulic system pressure is modulated by the proportional pressure control valve, and subsequently, the system pressure acts directly on a volume reinforcement slider, which possesses no pressure change means and which acts for the direct control of clutch in a motor vehicle transmission.
The proportional pressure control valve can be used as a pilot valve, as well as a direct control valve, in a hydraulic arrangement with a damper having a two stage characteristic curve. A following flow volume reinforcement slider connects on to said damper, that is, a slide for the minimizing of the pressure input upon the changeover from the holding phase into the operational phase.